Gaseous and particulate reactive nitrogen species in the indoor air of selected households in New Delhi.

Abstract

The present study reports the indoor abundance of inorganic trace gases (NH3, NO2 and SO2) and their corresponding particulates (NH4+, NO3- and SO42-) along with other major ionic species present in the aerosol form (Cl-, F-, Na+, K+, Ca2+ and Mg2+), in the urban households of megacity Delhi (India). Two different households (DH site and MH site) were selected in the city based on the variation in the land use patterns of the locations in which they were situated. Trace gases followed the order NH3 > SO2 > NO2 at both the sites with NH3 contributing about 90% and 85% to the total Nr species at DH and MH sites, respectively. NH3 showed maximum indoor concentrations during monsoon season whereas NO2 and SO2 were higher during winter season. The gas to particle conversion of the inorganic trace gases was studied by calculating their oxidation ratios which followed the order SOR > NOR > NHR, indicating that SO2 showed more oxidative conversion to SO42- as compared to NO2 and NH3 in the indoor setup. The chemical composition of the particulates revealed that Ca2+ and SO42- were the most abundant cation and anion, respectively, among the measured ionic species at both sites and the concentrations of all the major ions were higher for the industrial MH site as compared to the residential DH site. Source apportionment using principal component analysis and mass ratios showed that indoor activities such as cooking, cleaning along with others such as biomass burning and dust resuspension were responsible for the indoor composition of particulates at DH site whereas outdoor influences such as coal burning and industrial emissions from local sources were prominent at MH site due to its industrialized surroundings. For naturally ventilated households (such as the present study), it was observed that the emissions generated indoors as well as the characteristic outdoor influences seem to influence the overall indoor air composition and quality.